<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="UTF-8">
<title>Use of JQ focus selector</title>
<link rel="stylesheet" href="base.css" />
<script type="text/javascript" src="jquery-1.10.1.min.js" ></script>
</head>
<body>
<div style="width: 200px; margin: 20px auto 0 auto;">
姓名：<input name="name" type="text" label="姓名"><br>
年龄：<input name="age" type="text" label="年龄"><br>
手机：<input name="cellphone" type="text" label="手机">
</div>
<div id="message" style=" width: 200px; margin: 0 auto;"></div>
<script>
//: The focus selector is generally used in event processing to determine whether the specified element currently has the focus.
//In general, only elements that receive keyboard events or user input can gain focus, such as a form's <input> element.
$("input").on("focus blur", function(){
var me = $(this);
//When the <input> element gets the focus, the corresponding prompt information such as "Please enter [name]", "Please enter [age]" is displayed in #message.
var msg = me.is(":focus") ? ("请输入[" + me.attr("label") + "]") : "";
$("#message").html(msg);
});
</script>
</body>
</html>
Effect picture: